Indium tin-oxide (ITO) is traditionally widely used as a transparent conductor in transparent electrodes in science and research community, but it also has well drawbacks in large scale manufacturing processes. First, in order to make electrodes, ITO is vacuum deposited onto substrates, and the vacuum deposition process is expensive and low throughput. Second, in most of applications, 150 nm or thicker of ITO is needed to ensure electrical performance, but at such thicknesses, ITO films become brittle making them not feasible for applications requiring large areas or flexible substrates. Third, to achieve good conductivity and clarity, ITO films need to be annealed at high temperatures, preferably over 200 C, thus limiting its application on high temperature resistant substrates such as glass. Due to the low softening point of polymers, most polymer based ITO films cannot withstand the annealing temperatures required for achieving the high conductivity and transparency at the same time. Therefore as electro-optical applications expand to more novel and exotic functionalities, such as 3-dimensional displays and solar cells, there is an increasing demand to invent alternative transparent electrodes with better than or comparable optical and electrical performance of ITO but suitable for large area flexible substrate and can be manufactured in an inexpensive high through manner.
Transparent conductive electrodes comprising printable metal nanowires have been successfully demonstrated as alternatives to be manufactured at low cost and on a large scale and with excellent performance including conductivity and transparency.
However, most of the commercial available transparent electrode having metal nanowires embedded in a matrix. “Matrix” refers to a solid-state material into which the metal nanowires are dispersed or embedded. The matrix is a host for the metal nanowires and provides a physical form of the conductive layer. The matrix protects the metal nanowires from adverse environmental factors, such as corrosion and abrasion. In particular, the matrix significantly lowers the permeability of corrosive elements in the environment, such as moisture, trace amount of acids, oxygen, sulfur and the like.
In addition, the matrix offers favorable physical and mechanical properties to the conductive layer. For example, it can provide adhesion to the substrate. Furthermore, unlike metal oxide films, polymeric or organic polymers or pre-polymers have become a better matrix to embed metal nanowires, because they can be robust and flexible, which make it possible to fabricate transparent conductors in a low-cost, high throughput process.
But in general, the matrix materials are less conductive than metal nanowire network, or some matrix materials are not conductive at all. Embedding the virgin metal nanowires in a polymer matrix, reduces the conductivity of the film. Some electrode actually requires portions of the nanowires protrude from the matrix material to enable access to the conductive network, or to make it surface conductive.
In view of the foregoing, an alternative method to protect the metal nanowires and improve adhesion is need. Even when a matrix is to be used, a composition or method to improve the conductive of the matrix is also needed.